1. Field of the Invention
The present invention relates to an antenna array, and in particular relates to an omnidirectional antenna array.
2. Description of the Related Art
Conventionally, an omni directional dipole antenna is utilized for transmitting signals from different directions. However, the dipole antenna decreases gain value and transmission distance. To improve gain value of the dipole antenna, the dimension of the dipole antenna is increased. For example, a dipole antenna having a gain value of 11 dBi for transmitting a signal with a frequency of 0.8 GHz has a length of more than 300 cm.
US Pub. 2006/0273865 and U.S. Pat. No. 7,173,572 disclose microstrip antennas for transmitting signals from different directions. However, the conventional micro strip antenna is assembled with a holder or a supporting shelf. The cost and size of the conventional micro strip antennas are therefore relatively high.